1. Field of the Invention
The present invention relates to a method and apparatus for continuous and regular liberation of active constituents into water. It relates more particularly to a method and apparatus for continuous liberation of vitamin A into wells and boreholes which provide a source of drinking water.
2. Description of the Related Art
It is estimated that at present several tens of millions of persons have a vitamin A deficiency. This deficiency can result in xerophthalmia, blindness, lowered resistance to infection, and an increase of mortality. The parts of the world which are most affected are Africa, Asia and Latin America. Among these, the zones of the Sahel and the Southern Sahel, namely Benin, Burkina, Faso, Mali and Mauritania, are most gravely affected.
One of the actions being carried out at present by the World Health Organization is distribution of oral doses of 200,000 international units of vitamin A in capsule form twice a year. However, it is difficult to distribute the necessary dose of vitamin A biannually to each inhabitant of the effected areas. Therefore, it would be preferred to provide each inhabitant with vitamin A in a natural manner by means of drinking water. This requires a system for continuous liberation of vitamin A which is easy to implement and allows regular delivery of the vitamin A over prolonged periods. The apparatus used to supply the vitamin A should not need to be changed more than 3 or 4 times per year. This minimizes the number of times a person must visit water points which are often widely dispersed in these desert zones.
There exist numerous patents describing the regular liberation of active constituents, among them vitamins, in the human or animal body. Such patents include, for example, U.S. Pat. Nos. 3,946,734 and 3,977,404, and European Patent Nos. 40,457 and 262,422. These patents are not directed to the problem which the present invention attempts to solve.
There also exist patents which disclose an apparatus for regular liberation of active constituents into the surrounding medium. Such patents include, for example, U.S. Pat. Nos. 4,300,558 and 4,618,487, European Patent No. 40,457 and British Patent No. 2,182,559. These patents disclose an apparatus which establishes an osmotic difference between the interior of an apparatus, which contains the active constituent to be diffused and a mineral salt, and the exterior of the apparatus. The large quantity of salt attracts water from the exterior environment which enters through the wall of the apparatus. This water, along with the dissolved salt and the active constituent, escape through an orifice made in the wall of the apparatus. The exterior wall is generally permeable to water and impermeable to the active constituent.
Such an apparatus is disadvantageous because it requires the manufacture of a delivery system made of a semi-permeable material. It is also disadvantageous because it requires the use of a large quantity of mineral salt which will inevitably be liberated with the active constituent. In the case of the addition of an active constituent, such as vitamin A, to drinking water, it is desired to liberate the minimum amount of salt in order not to modify the taste of the water.